Changes

The most successful missions to date have been the Mars Excursion Rover missions. Two of these sophisticated mobile robots, named ''Spirit'' and ''Opportunity'', launched in 2003 and arrived safely on Mars about six months later, on opposite sides of the planet. They have been running for four years now, at least fifteen times longer than they were warranted to run. The Opportunity rover has been taking pictures of the Victoria Crater, and Spirit has been photographing the Esperanza formation which contains "vesicular" basalt (characterized by multiple cavities representing dissolved gas escaping from solution during a volcanic eruption).<ref name=David>David, Leonard. "[http://www.space.com/missionlaunches/061228_rovers_update.html Mars Rovers: On the Roll to New Targets]." ''Space.com'' December 28, 2006. Accessed May 27, 2008.</ref>

The most successful missions to date have been the Mars Excursion Rover missions. Two of these sophisticated mobile robots, named ''Spirit'' and ''Opportunity'', launched in 2003 and arrived safely on Mars about six months later, on opposite sides of the planet. They have been running for four years now, at least fifteen times longer than they were warranted to run. The Opportunity rover has been taking pictures of the Victoria Crater, and Spirit has been photographing the Esperanza formation which contains "vesicular" basalt (characterized by multiple cavities representing dissolved gas escaping from solution during a volcanic eruption).<ref name=David>David, Leonard. "[http://www.space.com/missionlaunches/061228_rovers_update.html Mars Rovers: On the Roll to New Targets]." ''Space.com'' December 28, 2006. Accessed May 27, 2008.</ref>

On May 26, 2008, NASA placed a polar lander on Mars for the first time: the [[Phoenix lander]]. As of May 28, 2008, the Phoenix lander is functioning well and is about to begin its program to sample the soil and ice where it rests.

On May 26, 2008, NASA placed a polar lander on Mars for the first time: the [[Phoenix lander]]. As of June 28, 2008, the Phoenix lander is functioning well and has already discovered water ice where it landed. Contrary to prior understandings, the Phoenix lander has found an alkaline soil that might be suitable for growing Earth vegetables.

At least one non-governmental group, calling itself the Mars Society, has been actively studying technologies appropriate to send a crew of from four to six astronauts to Mars for a roughly two-year stay.<ref name=marssoc>[http://www.marssociety.org/portal The Mars Society] global and USA portal. Accessed May 27, 2008.</ref>

At least one non-governmental group, calling itself the Mars Society, has been actively studying technologies appropriate to send a crew of from four to six astronauts to Mars for a roughly two-year stay.<ref name=marssoc>[http://www.marssociety.org/portal The Mars Society] global and USA portal. Accessed May 27, 2008.</ref>